It says the measure shouldn't have been set up as a single ballot issue because it contains two transportation measures and violates the one-man, one-vote principle by making some votes count more than others.

The legislation basically means "logrolling," said Jim Horn, chairman of the association, which opposes the measure and particularly opposes the light rail transit expansion it would bring.

The suit is the association's second attempted court challenge of the ballot measure; it tried to join a challenge brought to the State Supreme Court by a Spokane attorney, Steve Eugster, but the high court wouldn't allow the group to intervene and Eugster withdrew.

The measure includes light rail transit projects and road improvements, and in some cases, "in order to vote for something you want, you have to vote for something you don't want," Horn said.

The measure would impose additional sales and license-tab taxes to pay for additional light rail construction, as well as improvements to several major regional highways, including a new Evergreen Point Bridge.

Legislators and others argue the measure is legal. Last Friday two Superior Court judges upheld the ballot measure against separate challenges brought by a group made up mostly of Sierra Club members.

The Sierra Club, among other issues, argued that the measure violates a constitutional ban on legislation covering more than one subject. Their arguments on that issue and two others were rejected last week at about the same time the Eastside group filed its lawsuit.

The association also argues that the measure violates one-man, one-vote because it gives greater weight to voters in Sound Transit's service territory over the larger number of voters in the area voting on the highway project list proposed by the Regional Transportation Investment District.

Phil Talmadge, an association attorney and former State Supreme Court justice, said the measure also violates the state constitution by setting time limits for appeals and challenges to the law that set up the ballot "and that's not fair."

Legislators and Sound Transit officials have said the ballot measure is legal and the two parts of it are both about transportation and, thus, related.

Sound Transit spokesman Geoff Patrick said his agency is "confident in the constitutionality of the framework that the legislature established for the roads-and-transit ballot measure" but said his agency hadn't reviewed the lawsuit and declined further comment. Staffers at the state Attorney General's Office did not return messages Monday requesting comment.

The measure includes a $30.8 billion Sound Transit expansion proposal that would add 49 miles of light rail and other facilities, plus $16.1 billion in highway projects including the Evergreen Point Bridge, improvements to Interstate 405 and state Route 167 and widening and improvements to several major Seattle streets.

The initial cost estimates for the two parts of the measure were $10.8 billion for Sound Transit expansion and $7 billion for roads but the numbers rise to the larger totals when estimates for construction, inflation, interest and other debt payment costs incurred over several decades are factored in.